1. Field of the Invention
The present invention relates to a two-axial rotational driving apparatus which rotates a driven member such as an image-taking apparatus about two axes.
2. Description of Related Art
Conventionally, pan-tilt drive unit apparatuses have been used in which a driven member such as a monitoring camera can be rotationally driven in two-axial directions (for example, a pan direction and a tilt direction).
FIG. 4 shows a conventional pan-tilt drive unit apparatus. The pan-tilt drive unit apparatus has a support member 406 on which a monitoring camera, not shown, is mounted. The support member 406 can be rotated in a pan direction (a direction indicated by an arrow B) and a tilt direction (a direction indicated by an arrow A) (see Japanese Patent Application Laid-Open No. 2000-47292).
A decelerating mechanism 417 is coupled to a tilt motor 411 . The support member 406 is coupled to the decelerating mechanism 417. The support member 406 is rotated in the tilt direction about a rotation axis L1 upon reception of a driving force from the tilt motor 411 through the decelerating mechanism 417.
A decelerating mechanism 407 is coupled to a pan motor 401. A case 421 to which the support member 406 is fixed is coupled to the decelerating mechanism 407. When the pan motor 401 is driven, the case 421 is rotated in the pan direction about a rotation axis L2 together with the tilter motor 411 and the decelerating mechanism 417.
FIG. 5 shows another conventional pan-tilt drive unit apparatus. The pan-tilt drive unit apparatus also has a support member 506 on which a monitoring camera is mounted, and differs from the pan-tilt drive unit apparatus shown in FIG. 4 in a mechanism for rotation in a tilt direction.
Specifically, while the pan-tilt drive unit apparatus shown in FIG. 4 has the tilt motor 411 and the pan motor 401 arranged perpendicularly to each other, the pan-tilt drive unit apparatus shown in FIG. 5 has a pan motor 501 and a tilt motor 511 arranged side by side substantially in parallel with a rotation axis L2. This arrangement is used to minimize space (operation space) occupied by the pan-tilt drive unit apparatus rotating in a pan direction.
In FIG. 5, decelerating mechanisms 517A and 517B are coupled to the tilt motor 511, and the support member 506 is coupled to the decelerating mechanism 517B. A decelerating mechanism 507 is coupled to the pan motor 501, and a case 521 to which the support member 506 is fixed is coupled to the decelerating mechanism 507.
When the tilt motor 511 is driven, output from the tilt motor 511 (output for rotation in the pan direction) is converted into output for rotation in the tilt direction by the decelerating mechanisms 517A and 517B to rotate a driven member 506 in the tilt direction. When the pan motor 501 is driven, the case 521 to which the driven member 506 is fixed is rotated in the pan direction together with the tilt motor 511 and the decelerating mechanisms 517A and 517B.
In the conventional pan-tilt drive unit apparatuses described above, when a monitoring camera is mounted on the support member, the camera is preferably arranged on the rotation axes for pan and tilt (L1 and L2). This is because the camera can be rotated easily in an intended direction and the apparatus (a pan-tilt zoom unit apparatus) can be miniaturized as a whole.
In the pan-tilt drive unit apparatus shown in FIG. 4, if a camera is arranged on the rotation axes for pan and tilt (L1 and L2) and the pan motor 401 is driven, the tilt motor 411 is rotated in the pan direction together with the camera. Thus, the pan motor 401 is arranged at a position which does not overlies the rotation trajectory of the tilt motor 411 to avoid interference with the rotation of the tilt motor 411 in the pan direction.
On the other hand, in the pan-tilt drive unit apparatus shown in FIG. 5, the pan motor 501 and the tilt motor 511 are arranged substantially in parallel to reduce the space (operation space) occupied by the tilt motor 511 moving during rotation in the pan direction. Thus, in the pan-tilt drive unit apparatus, the operation space of the whole apparatus can be miniaturized as compared with the pan-tilt drive unit apparatus shown in FIG. 4.
Even in the pan-tilt drive unit apparatus shown in FIG. 5 having the pan motor 501 and the tilt motor 511 arranged in the same direction, however, it is still necessary to ensure space for arranging the pan motor 501 aside from the space occupied by the rotation trajectory of the tilt motor 511.
In other words, in each of the pan-tilt drive unit apparatuses shown in FIGS. 4 and 5, the minimum space required in addition to the space occupied by the driven member such as a camera includes the space for arranging the pan motor, the space for arranging the tilt motor, and the space for ensuring the rotation trajectory of the tilt motor.
In addition, in the pan-tilt drive unit apparatuses shown in FIGS. 4 and 5, the tilt motor is arranged only on one side of an output shaft of the pan motor, so that the mass centered on the output shaft of the pan motor is out of balance. Thus, highly accurate driving is difficult to achieve.
For example, high-definition cameras tend to have larger lenses to provide finer images. In association therewith, motors incorporated in pan-tilt drive unit apparatuses are increased in size.
To address this, a contemplated approach is to provide a weight on the opposite side to the tilt motor to adjust the mass balance around the output shaft of the pan motor. However, the pan motor requires a higher driving torque corresponding to the added weight, which represses a miniaturization in size of the pan motor.
These problems apply to a pan-tilt drive unit apparatus having a structure in which a pan motor is rotated together with a driven member when a tilt motor is driven.